Field of the Invention
This invention relates to a control device and control method for an internal combustion engine that controls a fuel injection amount according to an intake air quantity that is detected by an airflow meter.
Background Information
In general, the fuel injection amount of an internal combustion engine is controlled by detecting the intake air quantity per unit of time by an airflow meter that is disposed in an intake passage, and adjusting so as to have an appropriate air-fuel ratio (for example a theoretical air-fuel ratio) with respect to the intake air quantity per one cycle that is calculated from the intake air quantity per unit of time and the engine rotational speed. For example, an airflow meter that is provided immediately after an air cleaner is positioned away from an engine controller that carries out a step to calculate the fuel injection amount, and is connected to the engine controller via a wiring harness.
One example of the fuel injection amount of an internal combustion engine being controlled based on intake air quantity is disclosed in Japanese Laid-Open Patent Application No. 2009-270483, which discloses disposing a high-response type of airflow meter that can detect intake air pulsation or a momentary reverse flow in an intake passage.
As described above, since the airflow meter is connected to the engine controller via a wiring harness, there is the possibility that the signal path may be disconnected. Generally, some type of fail-safe mode is provided to counter the loss of the intake air quantity signal due to a disconnection of the airflow meter, in which the mode transitions to a fail-safe mode that does not depend on an airflow meter, such as simply obtaining the fuel injection amount from a throttle valve opening amount and the engine rotational speed, or fixing the throttle valve opening amount to a predetermined opening amount and inferring the intake air quantity according to the engine rotational speed.
However, a certain amount of delay time is necessary after the airflow meter is disconnected in order to transition to the fail-safe mode, including the time required for diagnosis so as to prevent an erroneous transition to the fail-safe mode due to noise, etc. Therefore, since a signal that gives an appearance that the intake air quantity is zero (or a negative flow) is output from the airflow meter during this delay time, the fuel injection amount becomes extremely small, and there is the possibility that a misfire may occur before transitioning to the fail-safe mode.